Star Formation in Galaxies

Star Formation in Galaxies - Star Formation in Galaxies...

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Star Formation in Galaxies Star formation is galaxy evolution caught in the act. Measurements of the star-formation rate (SFR) usually apply strictly only to OB stars and may be extrapolated to all masses, since less massive ones can't be distinguished from the older background population. Some observational indicators of star formation include: (1) Balmer and other recombination emission lines (2) Ultraviolet continuum emission from hot stars (3) Infrared thermal emission (reradiated starlight) (4) Radio continuum emission (free-free and nonthermal) (5) CO emission from molecular clouds (6) Integrated constraints from total optical luminosity. Recombination lines (especially Hα): Line emission is characteristic of H II regions, zones of ionized gas around young star clusters that still contain OB stars (spectral types B0.5 and hotter). These stars are special in that they are hot enough to produce significant fluxes of ionizing radiation, shortward of the Lyman limit. H II regions may be found wholesale by narrow-band imaging at Hα if internal extinction is not too large, and also by radio surveys for recombination- line emission (though this works best in our own galaxy). To turn measures of emission-line
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Star Formation in Galaxies - Star Formation in Galaxies...

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